The invention relates to a process for the preparation of methionine of high bulk density, in which a mixture which comprises a compound which has a foaming action and a compound which influences crystallization is added to the hydrolysis solution, and to the mixture itself.
It is known that the preparation of amino acids is often associated with difficulties. Handling of solutions or suspensions containing amino acids already leads to severe foaming in laboratory processes, but above all of course in industrial production. This undesirable effect can lead not only to the production proceeding in a very problematic manner and with poor space/time yields, but in individual cases also to failure of an economical production of the amino acid.
JP 09000241 thus describes that the addition of various additives from the family of nitrogen-containing polyoxyalkylenes in the fermentative production of amino acids leads to a reduction in foaming. JP 09000241 relates to the preparation of defoamer mixtures which are composed of fats or oils and the reaction products of fatty acids or derivatives thereof and polyalcohols with alkylene oxides. These mixtures are suitable for use in fermentations. It is known that the yield of lysine and tryptophan production can be increased if silicone are used as foam-destroying additives, instead of sunflower oil. The influence of various silicone oils is investigated by comparison in Khim.-Farm. Zh (1972), 6(5), 27–30.
In the carbonate process known from EP 0 780 370, methionine is obtained on acidification of a solution of potassium methioninate with carbon dioxide in accordance with the equation

Methionine is in general precipitated out of these solutions in the form of very flat leaflets, separating off of which proceeds only very slowly and therefore uneconomically.
There are therefore attempts to influence the crystallization properties of the methionine by addition of particular auxiliary substances.
It is demonstrated in JP-11-158140 that the use of various auxiliary substances, such as hydroxymethylpropylcellulose, sorbitan monolaurate or polyvinyl alcohols, influences the crystal habit, and the bulk density of the methionine obtained in this way increases.
These compounds are added in an amount of at least 500 ppm during the crystallization, which is carried out continuously and proceeds in two stages under specific stirring conditions. A round-particled methionine is obtained.
No additive or mixture of additives with the aid of which at the same time the foam which forms in the various stages of methionine preparation can be suppressed and the crystal habit of the methionine which has precipitated out, in particular in the carbonate process, can be improved is known from the prior art.